The invention relates to a ceramic composition on the basis of doped BaTiO.sub.3, which ceramic composition can suitably be used in capacitors. The invention also relates to a ceramic multilayer capacitor comprising a number of ceramic layers on the basis of a doped BaTiO.sub.3 as well as a number of electrode layers predominantly consisting of Ni, the ceramic layers and the electrode layers being alternately stacked to form a multilayer structure which is provided with electric connections at two side faces, said electric connections being connected to a number of the electrode layers. The invention further relates to a ceramic capacitor comprising two electrode layers predominantly consisting of Ni between which layers a dielectric ceramic layer on the basis of a doped BaTiO.sub.3 is situated.
Ceramic compositions of the type mentioned in the opening paragraph for use in monolithic ceramic capacitors are known per se. They are described, inter alia, in United States Patent document U.S. Pat. No. 5,264,402. This patent discloses, more particularly, non-reducible dielectric compositions consisting essentially of a modified barium titanate system, said main composition consisting essentially of oxides of Ba, Ca, Ti, Zr and Nb in a specific ratio, to which certain additives A and B have been added. This barium titanate (BaTiO.sub.3) system has a so-called perovskite structure. In the case of the known material, a specific quantity of Ca ions is substituted at the Ba sites of the perovskite structure, and specific quantities of Zr ions and Nb ions are substituted at the Ti sites.
The known ceramic compositions show interesting properties which make them suitable for use in so-called `base metal electrode` capacitors. Firstly, said compositions can be sintered in a reducing atmosphere at relatively low temperature. Therefore, instead of the expensive noble metal Pd the base metal Ni can be used for electrode layers. This relatively low sintering temperature is necessary to preclude that the Ni of the electrode layers melts during the sintering process. Secondly, said known compositions show a relatively high dielectric constant around 10000 and even higher, in combination with relatively low losses.
Capacitors, both of the monolithic type and of the multilayer type, which comprise said known ceramic composition as a dielectric show a clear disadvantage. It has been found that, in practice, the indicated composition does not lead to optimum properties of the capacitor. It has been shown that especially the electrical resistance of the known ceramic composition decreases rapidly if such capacitor is used at a relatively high temperature under direct current (dc) conditions.